168 ELEMENTS OF MAMMALIAN ANATOMY. 
The vagina extends from the uterus to the vestibule, 
opening on the surface ventrad to the anus. The small 
papilla just caudad of the orifice of the urethra on the 
ventral surface of the vestibule is the clitoris, the homo- 
logue of a part of the penis in the male. The prominent 
circular fold of mucous membrane craniad of the orifice of 
the urethra represents the /ymen, which marks the separa- 
tion between the vagina and vestibule. This structure may 
be shown by making a median longitudinal section through 
the vagina. SBartholin’s glands lie on the lateral aspect of 
the vestibule, into which their ducts open. Each one is 
about the size of a small pea. The vagina, uterus, and 
Fallopian tubes are lined with mucous membrane in which 
are many glands. The mucous lining is surrounded by a 
muscular coat especially thick in the uterus. 
The ovaries are the organs producing the female germ 
cells or ova which when fertilized are known as the eggs 
(Figs. 55 and 86). One lies caudad of the kidney on each 
side and is invested by peritoneum, which should be care- 
fully dissected away. A microscopically prepared section 
of the adult ovary magnified about 100 diameters will 
reveal a number of ova in a more or less mature state. 
Usually a peripheral ring of very young ova is present, 
more mature ones are near the center, while one or two 
quite ripe ova are very near the circumference. As the 
ova develop, a follicle or sac known as the Graafian follicle 
is formed about them. This is lined with several layers 
of epithelial cells forming the membrana granulosa. At 
one side of the follicle the membrana granulosa thickens 
and envelops the ovum, forming the discus proligerus. The 
cavity of the follicle is filled with liquor folliculi. When 
the ovum becomes almost mature, the walls of the follicle 
have grown peripherad, so as to cause a pin-head pro- 
tuberance on the surface of the ovary clearly visible to the 
